Add pre-commit hook installation to onboarding and upgrade processes

- prompts/onboarding.md: Step 2c installs git pre-commit hook for new projects
- scripts/upgrade.sh: Installs pre-commit hook during upgrade (with symlink detection)
- scripts/install.sh: Mentions hook installation in post-install next steps

scripts/install.sh

@@ -59,4 +59,10 @@ fi
 
 echo ""
 echo "Installation complete."
-echo "Next step: cd into a project and run the onboarding prompt."
+echo ""
+echo "Next steps:"
+echo "  1. cd into a project and run the onboarding prompt"
+echo "  2. In each project that uses git, install the pre-commit hook:"
+echo "     ln -sf ~/.automaton/scripts/git-hooks/pre-commit .git/hooks/pre-commit"
+echo ""
+echo "This hook blocks commits when no task is in an edit-allowed phase."